1. Field of the Invention
The present invention generally relates to a method of electing a leader in an ad-hoc network. More particularly, the present invention relates to a method of electing a leader node in an ad-hoc network capable of electing a suitable leader node in accordance with the circumstances such as the creation of an ad-hoc network, topology change of the ad-hoc network, and movement of a general node and the leader node.
2. Description of the Related Art
With the development of mobile communication appliances and communication techniques, in addition to the existing infrastructure network, the necessity for a small-sized wireless communication network has increased. Specifically, in environments where the network is isolated from an external Internet and no wire equipment is provided, for example, in a state of emergency, in an airplane, in a building, or in a mountainous region, a small-sized wireless communication network such as an ad-hoc network is greatly required.
In the ad-hoc network, unlike the infrastructure network, a router that repeats a packet transmission/reception does not exist separately, but each mobile node serves as a host and a router simultaneously. Since a node in the ad-hoc network is provided with wireless communication equipment, the movement of the node from one ad-hoc network to another network becomes possible, and this causes the topology of the ad-hoc network to be changed.
In the ad-hoc network, the transmission range of radio waves for each node is limited, and thus a packet may not be directly transmitted from its departure node to its destination node. In this case, the packet is transmitted via a plurality of nodes that serve as routers. This system is called a multi-hop system, and a routing protocol for implementing the multi-hop system is required in the ad-hoc network.
A node that takes part in the ad-hoc network should be allocated with an address to be used in the corresponding ad-hoc network. For this, the node generates a temporary address in the same manner as an automatic address generation, and performs a Duplicate Address Detection (DAD) to confirm whether the generated address is the sole address in the corresponding ad-hoc network.
The DAD starts when the node floods a Neighbor Solicitation (NS) message that includes an address generated by the node itself into the whole network, and succeeds if the node fails to receive a Neighbor Advertisement (NA) message from a node that uses the same address within a time limit. If the DAD succeeds, the corresponding node performs a communication in the ad-hoc network using the confirmed address.
Since a fixed router does not exist separately in the ad-hoc network and each node serves as a router and a host simultaneously, the communication between the nodes is performed without any central control. The communication between the nodes is performed in a manner that a departure node transmits a desired packet to the whole network and a designated destination node receives the packet directly or via another node.
Technical research in the ad-hoc network field has mainly been made with respect to an efficient routing method such as a method of supporting a network environment using an Internet Protocol (IP) that is an Internet addressing system. However, research for the configuration and management of an ad-hoc network is actively being performed.
Accordingly, by introducing the concept of a leader node for the configuration and management of the ad-hoc network, the DAD is efficiently performed in the ad-hoc network and an easy scalability of the network is sought by sending a Router Advertisement (RA) message.
There is no dominance among nodes that independently perform their communications as simultaneously serving as routers and hosts in the ad-hoc network. Thus, a leader node has to be elected among the nodes suitable to serve as a leader node in accordance with a certain method.
There is a conventional method of electing a leader node that gives a predetermined number to each node that takes part in the ad-hoc network as an Identification (ID) and elects the leader node by comparing such IDs with one another. However, since these IDs are given irrespective of the positions of each node according to the topology of the ad-hoc network, the leader node electing method does not reflect the topology of the network. Thus, the leader node elected by the conventional method cannot contribute to the transmission of the RA message and the shortening of time for the DAD performing transmission.
There is another conventional method, which elects a node having the largest number of neighbor nodes as a leader node. Such a leader node electing method uses information on neighbor nodes in order to elect the leader node, but it does not consider the topology of the whole ad-hoc network. Accordingly, it has the drawback in that it cannot reflect the topology of the whole ad-hoc network. When the leader node becomes unsuitable for its own role due to the change of the topology of the network and the change of the number of neighbor nodes for each node, because the leader node once elected cannot be replaced, the conventional method cannot cope with the change of the network topology.
In addition to the two above-described conventional methods of electing a leader node, there is another leader node electing method based on a Temporally-Ordered Routing Algorithm (TORA), that is, an ad-hoc routing protocol. However, this method, being based on a predetermined routing protocol, is inapplicable to other routing protocols except for the TORA.